Carbonaceous substances in solid, liquid as well as gaseous state are utilised as fuels for power engineering. In addition to well-known classical industrial fuels such as coke, oil, coal gas, etc. produced by traditional methods, fuels usable for power engineering are also acquired from various natural products, industrial waste, sorted household waste, sludge from sewage treatment plants, etc. Modern science and technology are increasingly concerned with issues of environmentally sound disposal of unwanted or waste materials and useful utilisation of carbonaceous sources contained there.
The usual way of processing of carbonaceous matters is thermolysis, i.e. thermal decomposition without combustion. Processed material is placed into a closed heated space such as a furnace chamber where it is subjected to high temperatures causing its decomposition and the gases being developed are discharged out from the heated space. Classic pyrolysis and other methods are involved. Gases discharged from the heated space are led through a heat exchanger or cooler, where they are subjected to cooling, which results in separation of water, if there is any, and oily condensate. The oily condensate is collected and further processed. Depending on the methods used and on collected fractions, it is utilisable directly or after further processing, especially as a lubricant and/or fuel. The gaseous medium remaining after separation of the condensate is led to devices serving for purification and concentration of utilisable gases and/or is used as fuel. Residual gaseous medium containing by now only nonutilizable waste products and possibly dust particles is led through filters into an exhaust pipe or chimney, or, in case of some methods and devices, it is led back to the heated space. Initial material based on organic residues, natural products, sludge, rubber, etc. is placed in a heated space in a container, trolley, on a sheet or other carrier, or is possibly fed on a grate positioned in the furnace chamber or other heating chamber. Material is preferably in a condition allowing good access of heat, i.e. in the form of chippings or particles obtained by grinding. Gases generated during the heating of material are changing their composition with increasing temperature of the material. First, ammonia and other volatile substances, water, inert gases, etc. are gradually released. It is known that gases with high content of hydrocarbons utilisable for power industry are released from these materials at temperatures varying with the initial material composition and pressure conditions. The principle of the process of thermal decomposition of these materials as well as the composition of fractions obtained by thermal decomposition depending on particular temperature and pressure of thermolysis is known. However, the problem is to achieve good economy of these thermal decomposition processes, i.e. the material heating mode, the amount of charge, the time of the material heat treatment, etc. The lack of optimal equipment is related to this as well. Heated chambers generally do not work continuously, it is necessary to cool them down before opening for each batch of raw material. Typically, the heating of heated space is stopped first and the heat is allowed to act for some time, then the space is allowed to cool naturally or it is artificially cooled. Gases may still leave the material after economic exhaustion of utilisable gaseous medium from processed material and during cooling, and therefore gases are usually drawn off even during this period, and then as the case may be, the still contained gases and/or swirling dust particles are drawn off after the space is sufficiently cooled to a safe temperature for opening. After the thermal process, usually only solid residue in the form of charred particles or of charred skeleton crumbling to rubble of coaly particles, whose prevailing component is carbon, remains from the initial batch of material in the workspace.
The abovementioned method is described for example in the patent application CZ PV 2010-586. Rubber waste is placed in a sealable chamber equipped with a heating element, cooling element, and a condensing circuit comprising a condenser. The rubber waste charge is in quantities from 0.1 to 0.9 of the volume of heated chamber. Subsequently, the chamber is closed and the temperature in the chamber is gradually increased to 350 to 400° C. without any specific modification of pressure conditions. Resulting gaseous products are led into a cooler where they partially condense and the condensate is collected in a separate tank. The cooled residual gaseous medium is led back into the chamber. After at least 40 minutes, but not before the rubber waste charge weight decreases by more than 15%, the space of the chamber is cooled to a temperature below 200° C. Subsequently, the chamber is opened and the resulting solid residue is removed. It consists of coke with residues of steel cord from tires. After removal of metal residues, this coke can be further utilised for example for heating. The device for implementation of the method comprises the chamber equipped with at least one heating element and cooling element, wherein the chamber is connected to the condensing circuit whose input and output is led into the chamber. The heating element consists of an electric heating spiral, which is due to the need to eliminate ignition of processed material placed in a protective housing and this unit is placed inside the heated chamber. There are for example four such heating elements inside the heated chamber according to the CZ PV 2010-586. From the outside, the chamber is provided with an insulating layer. In the abovementioned file, the pipe system of finned tubes placed in the heated chamber is described as the cooling element in the first example, and a partition wall situated on at least two sides of the chamber is described as the cooling element in the second example. Between the partition wall and the chamber wall, there is an air gap cooled by flowing air. Condensation circuit is equipped with a fan to provide circulation of gaseous medium from the chamber into the circuit and from the circuit back into the chamber, and it is furthermore equipped with a collecting vessel for condensate. The CZ PV 2010-586 describes the procedure for processing of worn down tires. Worn down tires are placed into the chamber in the quantity amounting to 60% of the chamber volume, and then the chamber is closed. The temperature in the chamber is gradually increased to 380° C. using the heating elements without special pressure adjustments. Resulting gases are led to the condensation circuit through which they circulate with the help of a fan and where condensate is created, collected and accumulated. After 40 minutes of thermal decomposition carried out in this way, the space of the chamber starts to cool down by supplying cooling medium into the cooling element. After cooling to 120° C., the chamber is opened and the resulting solid charred material residue is removed.
The disadvantage of the abovementioned method is that the gases developed during thermolysis are not processed by any other way than condensation. No utilisable combustible gas is extracted. Residual products contained in the chamber can escape into environment after opening the chamber. The method used and its thermal regime does not allow for sufficient decomposition of many raw materials. Repeated heating and cooling of the chamber separately for each batch of material is very uneconomical and results in large energy losses.
The document CZ U 21978 attempts to solve the abovementioned disadvantages of the said existing procedure. The heated chamber is equipped with an interchangeable mobile storage container, with the help of which the material intended for thermal decomposition is inserted into the heated chamber and removed from the chamber after the heat treatment. The mobile container is in the form of a mobile sealable body with a cover, which is equipped with a detachable inlet and outlet for gases generated by thermolysis. The said inlet and outlet are connected to the condensation circuit. The charge of material is gas-tightly separated from the heated chamber space by the cover. The procedure of material processing differs from the previous one in that the charge of material can be done into the hot chamber and the container with solid residues from thermal decomposition of the charge can be relocated out of the chamber while hot and allowed to cool outside the chamber on a suitable parking space, which significantly reduces the processing time for multiple charges in succession and also saves a lot of energy since shutdown and complete cooling down of the heated chamber are not necessary. The device and method described in this document already take into account also the option to disconnect the condensation circuit and divert the generated useful gas fractions for further utilisation and possible processing. The disadvantage is imperfect heat and pressure regime of decomposition, because it is impossible to set the optimum temperature curve of heating. Placing of material into the overheated-up chamber may cause undesired rapid development of gases leading to increased pressure in the system and as the case may be even to explosion, and also can give rise to a slag-like shell on the surface of the material, which prevents exit of generated gases. On the contrary, the chamber not heated up enough is rapidly cooled down with the newly inserted mobile container and thermal decomposition is inadequate. Sharp temperature fluctuations and distortions of the thermal process take place with each addition or removal of the mobile container into or out of the heated chamber. Even this device does not allow continuous process. The device is unable to generate utilisable gases in stable quantity and with stable composition. Possibility of connection of the device according to the CZ PV 2010-586 or the device according to the CZ U 21978 to a cogeneration unit is out the question also for the abovementioned reasons among others.
Document CZ U 21515 describes other device. The difference compared with the previous device is only in the fact that the gas pipeline for outlet of generated gasses is not emptying back into the heated chamber. A cooler with a receiver for condensate and with an outlet of residual gaseous exhausts out of the device is connected after the heated chamber. The mobile container used is only with a gas outlet, not with an inlet. Even in this case, the heated chamber of the device consists of a flameless furnace operating under normal atmospheric pressure, and also the mobile container operates likewise. The device operates similarly and has similar drawbacks as the previous one, with the difference that the residual gaseous medium is drawn off. The device operates only in a batch mode and therefore a sufficient quantity of gaseous and liquid products for the production of electricity and heat is not ensured. Another disadvantage is a problem with the purity and stability of directly manufactured gas when the gaseous fractions are released stepwise in the course of the thermal decomposition process of the charge with different material composition depending on increasing temperature, so that the composition of the gas produced varies with time. For use in a power unit however, it is necessary to use gas with a defined material composition that is constant within certain limits, so this device does not allow utilising the gas products as fuel in the energy unit. Due to temperature variations in the exhaust gas duct, its walls are frequently covered with the film of oleaginous substances from which these substances are subsequently partially released back into the gas, thereby polluting it. Also, the liquid product changes during the process of thermal decomposition of the charge both in quantity and quality, so that even the production of oily condensate cannot be used directly in the production as a fuel for a cogeneration unit or other combustion device.
Modern science also knows fast pyrolysis, for example the procedure and device that are described in the CZ Pat. 280 465 (with a priority from CA 90/2009021). Feedstock is heated up to a temperature of 350 to 800° C. with the lightning speed of 1,000 to 1,000,000° C./s, which is followed by a brief controlled dwell time, typically 30 ms to 2 s, and then rapid cooling of the product follows. Typically, the product is cooled rapidly below 350° C. within 0.5 s. Disadvantage of these processes is the need for expensive reactors, which are financially and spatially demanding. Configuration of these reactors is fundamentally different from the solved device, and therefore it will not be described herein.